1. Technical Field
The disclosure relates to a wireless power supply device which supplies electric power without contact, a wireless power receiving device which receives supply of electric power without contact, a wireless power transmission system including the wireless power supply device and the wireless power receiving device, and a method for protecting the wireless power receiving device from an excessive magnetic field.
2. Description of Related Art
In recent years, a wireless power transmission system, which wirelessly supplies electric power to a wearable apparatus such as a clock or an IC (Integrated Circuit) card by using an alternative magnetic field, has been commercialized. The wireless power transmission system includes a power transmission device which wirelessly transmits electric power via a power transmission coil that generates the alternative magnetic field, and a power receiving device which receives supply of electric power via a power receiving coil that converts the alternative magnetic field into the electric power.
Besides, a power transmission system, which performs various settings related to electric power transmission by performing data communication between the power transmission device and the power receiving device via the power transmission coil and the power receiving coil, is proposed as such wireless power transmission system (see Japanese Patent Application Laid-open No. 2016-111792 for example).
In this wireless power transmission system, a frequency of, for example, 13.56 MHz is adopted as the frequency of the alternative magnetic field used to perform the electric power transmission.
Meanwhile, when a foreign object exists between the power transmission device which performs power supply by such alternative magnetic field and an IC card which includes the power receiving device that receives the power supply, on the power transmission device side, the desired electric power is transmitted to the power receiving side in spite of the foreign object, leading to an increase of magnetic field strength. In this case, due to the strong magnetic field generated by the power transmission device, the IC card receiving the strong magnetic field generates heat beyond necessity and may be damaged.
Therefore, a non-contact electric power transmission device, which detects, on the power transmission device side, a current flowing through the power transmission coil, and stops the power transmission when the detected current value exceeds a predetermined threshold, is proposed (see Japanese Patent Application Laid-open No. 2016-92921 for example).
However, in the abovementioned non-contact electric power transmission device, in order to detect the current flowing through the power transmission coil, a current sensor is arranged in series between a power-supply line and a power transmission circuit, so that electric power loss is generated in the current sensor itself.